Water treatment

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Dalecarlia Water Treatment Plant, Washington, D.C. Dalecarlia Water Treatment Plant.jpg
Dalecarlia Water Treatment Plant, Washington, D.C.

Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.

Contents

Types

Drinking water treatment

Water contamination is primarily caused by the discharge of untreated wastewater from enterprises. The effluent from various enterprises, which contains varying levels of contaminants, is dumped into rivers or other water resources. The wastewater may have a high proportion of organic and inorganic contaminants at the initial discharge. Industries generate wastewater as a result of fabrication processes, processes dealing with paper and pulp, textiles, chemicals, and from various streams such as cooling towers, boilers, and production lines. [1]

Typical drinking water treatment processes Illustration of a typical drinking water treatment process.png
Typical drinking water treatment processes

Treatment for drinking water production involves the removal of contaminants and/or inactivation of any potentially harmful microbes from raw water to produce water that is pure enough for human consumption without any short term or long term risk of any adverse health effect. In general terms, the greatest microbial risks are associated with ingestion of water that is contaminated with human or animal (including bird) faeces. Faeces can be a source of pathogenic bacteria, viruses, protozoa and helminths. The removal or destruction of microbial pathogens is essential, and commonly involves the use of reactive chemical agents such as suspended solids, to remove bacteria, algae, viruses, fungi, and minerals including iron and manganese. Research including Professor Linda Lawton's group at Robert Gordon University, Aberdeen is working to improve detection of cyanobacteria. [2] These substances continue to cause great harm to several less developed countries who do not have access to effective water purification systems.[ original research? ]

Measures taken to ensure water quality not only relate to the treatment of the water, but to its conveyance and distribution after treatment. It is therefore common practice to keep residual disinfectants in the treated water to kill bacteriological contamination during distribution and to keep the pipes clean. [3]

Water supplied to domestic properties such as for tap water or other uses, may be further treated before use, often using an in-line treatment process. Such treatments can include water softening or ion exchange. [ citation needed ]

Wastewater treatment

This section is an excerpt from Wastewater treatment.[ edit ]
Sewage treatment plant (a type of wastewater treatment plant) in Cuxhaven, Germany 2012-05-28 Fotoflug Cuxhaven Wilhelmshaven DSCF9867 (crop).jpg
Sewage treatment plant (a type of wastewater treatment plant) in Cuxhaven, Germany

Wastewater treatment is a process which removes and eliminates contaminants from wastewater and converts this into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes (called water reclamation). [4] The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater (also called municipal wastewater or sewage), the treatment plant is called a Sewage Treatment. For industrial wastewater, treatment either takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant (usually after some form of pre-treatment). Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.

Processes commonly used in wastewater treatment include phase separation (such as sedimentation), biological and chemical processes (such as oxidation) or polishing. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant. [5] : Ch.14  Biogas can be another by-product if anaerobic treatment processes are used. Treated wastewater can be reused as reclaimed water. [6] The main purpose of wastewater treatment is for the treated wastewater to be able to be disposed or reused safely. However, before it is treated, the options for disposal or reuse must be considered so the correct treatment process is used on the wastewater. Bangladesh has officially inaugurated the largest single sewage treatment plant (STP) in South Asia, located in the Khilgaon area of the city. With a capacity to treat five million sewage per day, the STP marks a significant step towards addressing the country's wastewater management challenges. [7]

The term "wastewater treatment" is often used to mean "sewage treatment". [8]

Industrial water treatment

This section is an excerpt from Industrial water treatment § Overview.[ edit ]

Water treatment is used to optimize most water-based industrial processes, such as heating, cooling, processing, cleaning, and rinsing so that operating costs and risks are reduced. Poor water treatment lets water interact with the surfaces of pipes and vessels which contain it. Steam boilers can scale up or corrode, and these deposits will mean more fuel is needed to heat the same amount of water. Cooling towers can also scale up and corrode, but left untreated, the warm, dirty water they can contain will encourage bacteria to grow, and Legionnaires' disease can be the fatal consequence. Water treatment is also used to improve the quality of water contacting the manufactured product (e.g., semiconductors) and/or can be part of the product (e.g., beverages, pharmaceuticals). In these instances, poor water treatment can cause defective products.[ citation needed ]

In many cases, effluent water from one process can be suitable for reuse in another process if given suitable treatment. This can reduce costs by lowering charges for water consumption, reduce the costs of effluent disposal because of reduced volume, and lower energy costs due to the recovery of heat in recycled wastewater.
At Turun Seudun Vesi Oy's artificial groundwater plant, the pretreated raw water from the Kokemaki River is absorbed through the basins into the Virttaankangas ridge formation. Imeytysallas Virttaankankaan tekopohjavesilaitos.JPG
At Turun Seudun Vesi Oy's artificial groundwater plant, the pretreated raw water from the Kokemäki River is absorbed through the basins into the Virttaankangas ridge formation.

Processes

Empty aeration tank for iron precipitation Prazdna aeracni mistnost, UV Karany.jpg
Empty aeration tank for iron precipitation

For the elimination of hazardous chemicals from the water, many treatment procedures have been applied. [9]

The processes involved in removing the contaminants include physical processes such as settling and filtration, chemical processes such as disinfection and coagulation, and biological processes such as slow sand filtration.

A combination selected from the following processes (depending on the season and contaminants and chemicals present in the raw water) is used for municipal drinking water treatment worldwide.

Chemical

Tanks with sand filters to remove precipitated iron (not working at the time) Piskove rychlofiltry odzelezovny v Karanem v klidu.jpg
Tanks with sand filters to remove precipitated iron (not working at the time)

Different chemical procedures for the conversion into final products or the removal of pollutants are used for the safe disposal of contaminants. [10]

Physical

Physical techniques of water/waste water treatment rely on physical phenomena to complete the removal process, rather than biological or chemical changes. [10]

Most common physical techniques are:

Physico-chemical

Also referred to as "Conventional" Treatment

Chemical precipitation is a common process used to reduce heavy metals concentrations in wastewater. The dissolved metal ions are transformed to an insoluble phase by a chemical interaction with a precipitant agent such as lime. In industrial applications stronger alkalis may be used to effect complete precipitation. In drinking water treatment, the common-ion effect is often used to help reduce water hardness. [15]

Flotation uses bubble attachment to separate solids or dispersed liquids from a liquid phase. [16]

Membrane filtration

Membrane filtration has gotten a lot of attention for inorganic effluent treatment since it can remove not only suspended solids and organic components, but also inorganic pollutants such heavy metals. For heavy metal removal, several forms of membrane filtration, such as ultrafiltration, nanofiltration, and reverse osmosis, can be used depending on the particle size that can be maintained. [17] [18]

Ion exchange

Ion exchange is a reversible ion exchange process in which an insoluble substance (resin) takes ions from an electrolytic solution and releases additional ions of the same charge in a chemically comparable amount without changing the resin's structure. [19] [20]

Electrochemical treatment techniques

[18]

  • Electrodialysis (ED)
  • Membrane electrolysis (ME)
  • Electrochemical precipitation (EP)

Adsorption

Adsorption is a mass transfer process in which a substance is transported from the liquid phase to the surface of a solid/liquid (adsorbent) and becomes physically and chemically bonded (adsorbate). Adsorption can be classified into two forms based on the type of attraction between the adsorbate and the adsorbent: physical and chemical adsorption, commonly known as physisorption and chemisorptions. [21] [22]

Activated carbon

Activated carbons (ACs) or biological-activated carbon (BAC) [23] are effective adsorbents for a wide variety of contaminants. The adsorptive removal of color, aroma, taste, and other harmful organics and inorganics from drinking water and wastewater is one of their industrial applications. [24]

Both a high surface area and a large pore size can improve the efficiency of activated carbon. Activated carbon was utilized by a number of studies to remove heavy metals and other types of contaminants from wastewater. The cost of activated carbon is rising due to a shortage of commercial activated carbon (AC). Because of its high surface area, porosity, and flexibility, activated carbon has a lot of potential in wastewater treatment. [24]

Biological

This is the method by which dissolved and suspended organic chemical components are eliminated through biodegradation, in which an optimal amount of microorganism is given to re-enact the same natural self-purification process. [25] Through two distinct biological process, such as biological oxidation and biosynthesis, microorganisms can degrade organic materials in wastewater. Microorganisms involved in wastewater treatment produce end products such as minerals, carbon dioxide, and ammonia during the biological oxidation process. The minerals (products) remained in the wastewater and were discharged with the effluent. Microorganisms use organic materials in wastewater to generate new microbial cells with dense biomass that is eliminated by sedimentation throughout the biosynthesis process. [26]

Standards

Many developed countries specify standards to be applied in their own country. In Europe, this includes the European Drinking Water Directive [27] and in the United States the United States Environmental Protection Agency (EPA) establishes standards as required by the Safe Drinking Water Act. For countries without a legislative or administrative framework for such standards, the World Health Organization publishes guidelines on the standards that should be achieved. [28] China adopted its own drinking water standard GB3838-2002 (Type II) enacted by Ministry of Environmental Protection in 2002. [29]

Where drinking water quality standards do exist, most are expressed as guidelines or targets rather than requirements, and very few water standards have any legal basis or, are subject to enforcement. [30] Two exceptions are the European Drinking Water Directive and the Safe Drinking Water Act in the United States, which require legal compliance with specific standards.

Developing countries

Appropriate technology options in water treatment include both community-scale and household-scale point-of-use (POU) or self-supply designs. [31] Such designs may employ solar water disinfection methods, using solar irradiation to inactivate harmful waterborne microorganisms directly, mainly by the UV-A component of the solar spectrum, or indirectly through the presence of an oxide photocatalyst, typically supported TiO2 in its anatase or rutile phases. [32] Despite progress in SODIS technology, military surplus water treatment units like the ERDLator are still frequently used in developing countries. Newer military style Reverse Osmosis Water Purification Units (ROWPU) are portable, self-contained water treatment plants are becoming more available for public use. [33]

For waterborne disease reduction to last, water treatment programs that research and development groups start in developing countries must be sustainable by the citizens of those countries. This can ensure the efficiency of such programs after the departure of the research team, as monitoring is difficult because of the remoteness of many locations.

Energy Consumption: Water treatment plants can be significant consumers of energy. In California, more than 4% of the state's electricity consumption goes towards transporting moderate quality water over long distances, treating that water to a high standard. [34] In areas with high quality water sources which flow by gravity to the point of consumption, costs will be much lower. Much of the energy requirements are in pumping. Processes that avoid the need for pumping tend to have overall low energy demands. Those water treatment technologies that have very low energy requirements including trickling filters, slow sand filters, gravity aqueducts.

A 2021 study found that a large-scale water chlorination program in urban areas of Mexico massively reduced childhood diarrheal disease mortality rates. [35]

Materials

Stainless steels, such as Type 304L and 316L, are used extensively in the fabrication of water treatment plants due to their corrosion resistance to water and to the corrosivity of chlorination used for disinfection. [36] [37]

See also

Related Research Articles

<span class="mw-page-title-main">Water purification</span> Process of removing impurities from water

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The history of water purification includes a wide variety of methods. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.

Ultrafiltration (UF) is a variety of membrane filtration in which forces such as pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate (filtrate). This separation process is used in industry and research for purifying and concentrating macromolecular (103–106 Da) solutions, especially protein solutions.

<span class="mw-page-title-main">Wastewater treatment</span> Converting wastewater into an effluent for return to the water cycle

Wastewater treatment is a process which removes and eliminates contaminants from wastewater and converts this into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes. The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater, the treatment plant is called a Sewage Treatment. For industrial wastewater, treatment either takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant. Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.

<span class="mw-page-title-main">Reclaimed water</span> Converting wastewater into water that can be reused for other purposes

Water reclamation is the process of converting municipal wastewater (sewage) or industrial wastewater into water that can be reused for a variety of purposes. Types of reuse include: urban reuse, agricultural reuse (irrigation), environmental reuse, industrial reuse, planned potable reuse, and de facto wastewater reuse. For example, reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater. Reused water may also be directed toward fulfilling certain needs in residences, businesses, and industry, and could even be treated to reach drinking water standards. The injection of reclaimed water into the water supply distribution system is known as direct potable reuse. However, drinking reclaimed water is not a typical practice. Treated municipal wastewater reuse for irrigation is a long-established practice, especially in arid countries. Reusing wastewater as part of sustainable water management allows water to remain as an alternative water source for human activities. This can reduce scarcity and alleviate pressures on groundwater and other natural water bodies.

<span class="mw-page-title-main">Industrial wastewater treatment</span> Processes used for treating wastewater that is produced by industries as an undesirable by-product

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.

<span class="mw-page-title-main">Sand filter</span> Water filtration device

Sand filters are used as a step in the water treatment process of water purification.

Electrocoagulation (EC) is a technique used for wastewater treatment, wash water treatment, industrially processed water, and medical treatment. Electrocoagulation has become a rapidly growing area of wastewater treatment due to its ability to remove contaminants that are generally more difficult to remove by filtration or chemical treatment systems, such as emulsified oil, total petroleum hydrocarbons, refractory organics, suspended solids, and heavy metals. There are many brands of electrocoagulation devices available, and they can range in complexity from a simple anode and cathode to much more complex devices with control over electrode potentials, passivation, anode consumption, cell REDOX potentials as well as the introduction of ultrasonic sound, ultraviolet light and a range of gases and reactants to achieve so-called Advanced Oxidation Processes for refractory or recalcitrant organic substances.

There are many uses of water in industry and, in most cases, the used water also needs treatment to render it fit for re-use or disposal. Raw water entering an industrial plant often needs treatment to meet tight quality specifications to be of use in specific industrial processes. Industrial water treatment encompasses all these aspects which include industrial wastewater treatment, boiler water treatment and cooling water treatment.

Advanced oxidation processes (AOPs), in a broad sense, are a set of chemical treatment procedures designed to remove organic (and sometimes inorganic) materials in water and wastewater by oxidation through reactions with hydroxyl radicals (·OH). In real-world applications of wastewater treatment, however, this term usually refers more specifically to a subset of such chemical processes that employ ozone (O3), hydrogen peroxide (H2O2) and/or UV light.

Green nanotechnology refers to the use of nanotechnology to enhance the environmental sustainability of processes producing negative externalities. It also refers to the use of the products of nanotechnology to enhance sustainability. It includes making green nano-products and using nano-products in support of sustainability.

<span class="mw-page-title-main">Sewage treatment</span> Process of removing contaminants from municipal wastewater

Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage,  using aerobic or anaerobic biological processes. A so-called quarternary treatment step can also be added for the removal of organic micropollutants, such as pharmaceuticals. This has been implemented in full-scale for example in Sweden.

Membrane bioreactors are combinations of some membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. These technologies are now widely used for municipal and industrial wastewater treatment. The two basic membrane bioreactor configurations are the submerged membrane bioreactor and the side stream membrane bioreactor. In the submerged configuration, the membrane is located inside the biological reactor and submerged in the wastewater, while in a side stream membrane bioreactor, the membrane is located outside the reactor as an additional step after biological treatment.

Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances, and is used in industrial processes and the production of potable water. RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. It relies on the relative sizes of the various molecules to decide what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules.

<span class="mw-page-title-main">Membrane</span> Thin, film-like structure separating two fluids, acting as a selective barrier

A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Biological membranes include cell membranes ; nuclear membranes, which cover a cell nucleus; and tissue membranes, such as mucosae and serosae. Synthetic membranes are made by humans for use in laboratories and industry.

Biosorption is a physiochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure. Biosorption can be defined as the ability of biological materials to accumulate heavy metals from wastewater through metabolically mediated or physico-chemical pathways of uptake. Though using biomass in environmental cleanup has been in practice for a while, scientists and engineers are hoping this phenomenon will provide an economical alternative for removing toxic heavy metals from industrial wastewater and aid in environmental remediation.

Raw water is water found in the environment that has not been treated and does not have any of its minerals, ions, particles, bacteria, or parasites removed. Raw water includes rainwater, ground water, water from infiltration wells, and water from bodies like lakes and rivers.

<span class="mw-page-title-main">Water reuse in California</span>

Water reuse in California is the use of reclaimed water for beneficial use. As a heavily populated state in the drought-prone arid west, water reuse is developing as an integral part of water in California enabling both the economy and population to grow.

Contaminants of emerging concern (CECs) is a term used by water quality professionals to describe pollutants that have been detected in environmental monitoring samples, that may cause ecological or human health impacts, and typically are not regulated under current environmental laws. Sources of these pollutants include agriculture, urban runoff and ordinary household products and pharmaceuticals that are disposed to sewage treatment plants and subsequently discharged to surface waters.

There are many water purifiers available in the market which use different techniques like boiling, filtration, distillation, chlorination, sedimentation and oxidation. Currently nanotechnology plays a vital role in water purification techniques. Nanotechnology is the process of manipulating atoms on a nanoscale. In nanotechnology, nanomembranes are used with the purpose of softening the water and removal of contaminants such as physical, biological and chemical contaminants. There are variety of techniques in nanotechnology which uses nanoparticles for providing safe drinking water with a high level of effectiveness. Some techniques have become commercialized.

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  35. ↑ Bhalotra, Sonia R.; Diaz-Cayeros, Alberto; Miller, Grant; Miranda, Alfonso; Venkataramani, Atheendar S. (2021). "Urban Water Disinfection and Mortality Decline in Lower-Income Countries". American Economic Journal: Economic Policy. 13 (4): 490–520. doi:10.1257/pol.20180764. ISSN   1945-7731. S2CID   236955246.
  36. ↑ R.E. Avery, S. Lamb, C.A. Powell and A.H. Tuthill. "Stainless Steels for Potable Water Treatment Plants". Nickel Institute.{{cite web}}: CS1 maint: multiple names: authors list (link)
  37. ↑ A.H. Tuthill and S. Lamb. "Guidelines for the use of Stainless Steel in Municipal Waste Water Treatment Plants". Nickel Institute.
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